Gather all your ingredients and tools. It’s important to have everything ready before you start, as the process moves quickly.

Crack open your room temperature egg and place it in a wide-mouth jar or food processor.

Add the oil, mustard, vinegar, and salt. If you’re using fresh lemon juice, add it now. You can also add garlic or herbs for a flavored mayo.

Place the immersion blender at the bottom of the jar. Begin blending on low speed, slowly lifting the blender as the mayo thickens. This should take just a few seconds.

Once the mayo has thickened, taste and adjust seasoning. If it’s too thick, you can add a little cold water to thin it out to your desired consistency.

Transfer the mayonnaise to an airtight container and refrigerate. It’s best used within a week, so make only what you need.